This present invention is concerned with a method of forming a plain bearing lining.
Plain bearings are widely used for supporting rotating shafts, eg they are used for supporting the crank shafts of internal combustion engines. Such plain bearings have a lining which is formed front a soft metal, ie a metal having a hardness of less than 100 Hv. The soft metal is able to accommodate misalinements between the bearing and the shaft and, also, is able to cope with particles of dirt which become embedded in the Fecal rather than Scratching the shaft. Originally, the soft metal bearing lining was cast into a housing but now such bearing linings are normally applied to a strong backing support, eg of steel or bronze, by methods such as so-called roll-bonding, strip casting and sintering for example. Suitable metals for forming the lining include lead-based, tin-based and cadmium-based white metal alloys (Babbitt), copper-based alloys (particularly copper-lead and copper-lead-tin), and aluminium-based alloys (particularly aluminium-tin, aluminium-tin-copper, aluminium-silicon-tin, and aluminium-tin-copper-silicon alloys for example).
Conventionally, bearing linings made of aluminium-based alloys are applied to their backing support by roll bonding in strip form and are then formed into half-bearings and machined to their final shape. Other soft metal bearing linings are cast or sintered on to their support backing material. However, plain bearings made by these methods have limited strength and the application methods are complex. Furthermore, the methods employed for the manufacture of half-bearings arc not suitable for applying the bearing lining material directly to a component having a complex shape.
Attempts have been made in the prior art to employ physical vapour deposition spraying processes such as flame and plasma-arc spraying to deposit bearing lining materials, mainly aluminium-based, onto a backing substrate. However, such spraying processes have all suffered from the same disadvantages of high oxide content in the range of 10 to 20 weights due to oxidation of the molten or partially molten material and high levels of porosity in the region of 10 to 15xc2x0.
GB-A-1083003 is an example of one such process as described above and has the disadvantages described.
GB-A-2130250 is another example of a thermal spraying process but which also suffers from the disadvantages of high levels of oxidation and porosity.
Many of the prior spraying processes were attempts to overcome the particular segregation difficulties associated with the production by casting and roll-bonding of bearing linings comprising an aluminium matrix having particles of lead therein rather than for any intrinsic benefits that such deposition processes may have.
It is an object of the present invention to provide a method of forming a plain bearing lining which is simpler, produces stronger linings, and can be utilised to apply a lining directly to a component such as the bore of a connecting rod for an internal combustion engine for example.